The perception of air pollution and its health risk: a scoping review of measures and methods

ABSTRACT Background Although there is increasing awareness of the health risks of air pollution as a global issue, few studies have focused on the methods for assessing individuals’ perceptions of these risks. This scoping review aimed to identify previous research evaluating individuals’ perceptions of air pollution and its health effects, and to explore the measurement of perceptions, as a key resource for health behaviour. Methods The review followed the methodological framework proposed by Arksey and O’Malley. PubMed and Web of Science were searched. After initial and full-text screening, we further selected studies with standardised scales that had previously been tested for reliability and validity in assessing awareness and perceptions. Results After full-text screening, 95 studies were identified. ‘Perception/awareness of air quality’ was often measured, as well as ‘Perception of health risk.’ Only nine studies (9.5%) used validated scaled questionnaires. There was considerable variation in the scales used to measure the multiple dimensions of risk perception for air pollution. Conclusion Few studies used structured scales to quantify individuals’ perceptions, limiting comparisons among studies. Standardised methods for measuring health risk perception are needed.


Background
Risk perception refers to individuals' assessments and judgements towards potential hazards [1], which involves subjective cognitive processes and individuallevel factors, such as a person's experiences, feelings, knowledge, and beliefs, as well as scientific judgement.Risk perception is a key component in the formation of attitudes towards policies, as well as individuals' behaviours.A number of studies have focused on the effects of risk perception on specific health-protective actions, and it is widely accepted that risk perception is a determinant of changes in health behaviour [2].For example, previous studies have suggested an association between risk perception regarding infectious diseases and preventive behaviours, such as vaccination [3], travel avoidance [4], and distancing behaviours in response to infectious diseases [5].
Other studies have examined risk perception of environmental hazards, such as flooding [6], climate change [7], and radiation [8].It has been reported that risk perception of a specific environmental hazard can affect individuals' behaviours regarding avoidance of the associated health consequences [9,10] and modify their attitudes towards specific policies to reduce the population risk [11,12].There are arguments both for and against the use of risk perceptions in policy [13][14][15].
Regarding environmental hazards, in recent years there have been an increasing number of studies focusing on the risk perception of air pollution [16].Individuals' behaviours and intentions regarding the prevention of exposure to air pollution depend on how they perceive the health risks associated with air pollutants.One previous study showed that the perceived severity of air pollution-related health risks was associated with behavioural changes, including changing the duration and intensity of outdoor activity and the usage of air purifiers [17].Another survey conducted in Singapore examined respondents' risk perception regarding haze pollution, the primary source of which was forest fires in Southeast Asia; the results suggested that attention to media, interpersonal discussions, and knowledge played important roles in shaping individuals' risk perception regarding haze, and changed people's attitudes towards taking preventive measures [18].These results provide important evidence supporting health policies to raise public awareness about air pollution and encouraging preventive behaviours.
The heterogeneity in the results in existing studies of risk perception of air pollution and its health risks may originate from differences in the methods used to characterise individuals' risk perception, given the nature of subjective assessment and judgement.Additionally, risk perception has various conceptual dimensions [16].Most previous studies have focused on the specific dimensions of risk perception, which makes comparisons among studies difficult.Exploring the methodologies used for assessing risk perception of air pollution in previous studies may be useful for facilitating our understanding of the processes of behavioural change in the context of air pollution and health.Therefore, the current study aimed to identify literature evaluating people's perceptions of the health risks of air pollution and to explore the methodologies used in these previous studies.Specifically, we focused on the scales sin the studies and addressed the following research questions.
(1) What are the available scales for measuring the perception of air pollution and its health risks?(2) Which dimensions of perception do the scales measure?
We also explored the availability of scales targeting children because scales designed for adults may not always be applicable to children without modification.

Methods
We followed a five-stage methodological framework that was initially outlined by Arksey and O'Malley [19] and further advanced by Levac [20].

Literature search
We searched PubMed and Web of Science using the following keywords: air pollution ('air pollution', 'air quality'), perception ('perception', 'perceived health risk', 'perceived risk') and awareness ('awareness').The literature search was restricted to articles published between 1 January 1970 and 15 March 2022.Non-English language articles and grey literature were not included.

Study selection
We included original studies evaluating the perception of health risk from outdoor air pollution.Articles evaluating awareness, concerns, attitude and behaviour were also included as far as these concepts were related to outdoor air pollution or air quality.

Data extraction, processing, and reporting
For each article included in the analysis, we extracted the following data: bibliographic information, study objectives, study area and time period, participants' demographic information, sample size, and the methods of the survey.We classified the region according to 'Our World in Data.'We extracted the key dimensions of perceptions related to health risks from air pollution: 'perception of health risk,' which was considered to reflect a person's beliefs, judgements, and feelings [14]; 'perception/awareness of air quality,' which was considered to reflect a person's tendency to think about or be informed about the level of air quality [21], 'attitude,' which was considered to refer to the degree of a person's favourable/unfavourable evaluation of a particular behaviour [22], 'knowledge' about air pollution and health, and 'behavioural intention,' which was considered to refer to the degree to which a person is inclined to engage in a particular behaviour [22].
To focus on the scales measuring perception/ awareness of air pollution and its associated risks, we selected studies that used 'validated scales,' which have been previously tested for reliability and validity, or those that were used more than once in previous studies, so that comparisons between the studies were possible.
We synthesised the data descriptively and presented the results in the form of tables.

Results
The search identified 1,193 articles in PubMed and 1,578 articles in Web of Science Figure 1 presents a flow diagram of the selection process.After removing the duplication (n = 342), initial title and abstract screening identified 201 eligible articles.We obtained and reviewed the full-text, and finally included 95 articles in the analysis (Table S1).

Overview of the included studies
Table 1 shows a summary of the included articles.Although the study areas covered six continents, more than half of the studies were conducted in China  and the United States [21,[48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67].We identified two studies that were conducted in a multicountry setting, namely in seven European countries [68] and in 10 countries across multiple continents during the coronavirus 2019 pandemic; the results revealed that people from different countries were aware of air quality improvement during the implementation of coronavirus disease 2019-related restrictions [69].The number of articles gradually increased over time, reaching a high of 13 in 2017 (Figure 2).Although most of the earlier studies were conducted in Europe and North America, studies conducted in Asia were most common from the 2010s onwards.We also summarised data for the years in which the surveys were conducted.The time lag from the year of survey until the publication ranged from 0 to 14 years, with a median duration of 3 years (Table 1).However, 10 studies did not clearly report the year of the survey in the manuscript [48,61,[70][71][72][73][74][75][76][77].

Dimension of health risk perception measured
On the basis of the terms used in the articles, we extracted the key dimensions of perception related to health risks from air pollution (Table 2).Questions about perception/awareness of air quality were observed with the highest frequency, followed by questions about the perception of health risk, knowledge, behavioural intention, and attitude.

Scales of risk perception measuring various dimensions
Among these 95 studies, validated scales of risk perception were used in only nine articles (Table 3), which included studies from China [35,41,44,96], the United States [58,59], Croatia [89], Mexico [97], and France [91].Most of the scales [39,44,58,97] were specific to each study site.We summarised individual scales (Table 3, Table S2) and focused on the dimensions evaluated in each scale in the process from perception of air pollution to perception of health risks and subsequent behaviour to avoid those risks (Table 4).Among the nine studies mentioned above, perception of health risk was the most frequently evaluated dimension [35,39,41,59,89,91].A few studies [35,41] asked the health risk posed by air pollution using the validated questionnaires adapted from the previous studies to assess risk perception of other environmental hazards, such as climate change [119] and nuclear power [120,121].WHOQOL-BREF and SF-36, measuring perceived health and QOL, do not necessarily inquire about health risk perception related to air pollution.Thus, additional questions regarding air pollution were included in the studies [89,91].Three studies using scales to measure the dimensions of attitude [35,39,41], the dimension of knowledge was also measured.The content and quantity of questions measuring the dimension of knowledge vary across studies.While AHRKAAS has 25 detailed items that ask the knowledge about various aspects of air pollution (haze), from its sources to health impacts [44], BRFSS focused on the knowledge of the air quality index/alert, which could lead to behavioural response [97].There are two scales measuring behaviour dimensions [35,97], and the questions concerning specific behaviours differed between them.One scale asked the behaviours to reduce outdoor activities to avoid air pollution [97] while other measured information seeking behaviours [35].

Discussion
In the current scoping review, we identified 95 studies evaluating perceptions of the risk related to air pollution.The number of studies focusing on the perception of air pollution and its health risks has been increasing over time.Since the mid-2010s, the majority of studies investigating this topic have been conducted in Asia, led by China.This may be at least in part because air pollution emissions dramatically increased in these regions with rapid industrialisation and urbanisation.Additionally, media reporting on the extremely high levels of air pollution levels in some parts of Asia increased public concern about health risk from air pollutants.Air pollution is not only a local issue, but also a global issue.Recently, several studies have been conducted in Africa [73,92,96,103] and South America [97,104] where rapid economic development is advancing (Table 1, Figure 2).The study areas are generally affected by air pollutants from heavy traffic and odorous industrial emissions, and most of the studies have emphasised the importance of knowledge about air quality [73,92,97,103].Global-scale studies using standardised scales to measure the perception of air pollution and its health risks are essential for elucidating the common factors affecting individuals' perceptions regarding air quality and its health risks.However, few studies have been conducted across multiple countries.

Standardised scales
Only nine studies used standardised scales for which validity and reliability has been evaluated and tested [35,41,44,58,59,89,91,96,97].There is considerable variation among standardised scales for measuring the multiple dimensions of risk perception for air pollution, and none of the studies in the present review used the same scales.Table 4 illustrated the dimensions measured within each study's scale, including the perception of health risk, perception/awareness of air quality, attitudes, knowledge, and behavioural intention.However, the response indicators used different scales, including binary variables and 3-5-point Likert scales.
Additionally, the terms used in the scale vary among the studies, which makes comparisons among studies difficult.Although the objectives vary between studies, using a standardised scale may facilitate understanding of the process of health behavioural change.This may also elucidate the local attributes that influence risk perception when there are regional differences in the risk perception of air pollution.Standardised scales are even more important in studies conducted to evaluate the effectiveness of interventions.Although WHOQOL-BREF and SF-36 have been used in the field of public health, they are not necessarily used to examine perceived health related to air pollution.Most of the available scales, except for WHOQOL-BREF and SF-36, were developed in a local context, assuming a specific source of pollution in the area.For example, the BRFSS and CCAHS focused on local air pollution.In a study conducted in China [35], participants were asked how they perceived the seriousness of air pollution not only for the local community but also for the whole country, and for the world.Regarding these questions, it can be assumed that the researchers themselves see air pollution as a wider regional or global problem rather than a local issue.Creating a scale that can be used at the global scale to measure perceptions of air pollution worldwide may facilitate the comparison of the results among studies.

Scale for children
Fewer than 15% of the studies included in the current review involved adolescents and children (Table 1).
Children are more susceptible to air pollution than adults.Improving children's health literacy is considered to be increasingly important.WHOQOL-BREF and SF-36 have been used in studies of perceived QOL for adults.
A standardised scale has also been developed for measuring perceived QOL among children.In this review, we did not identify any studies that measured the perceived QOL for children using a standardised scale, such as the Paediatric Quality of Life Inventory [122].The AHRKAAS has been used in China [44] with a focus on adolescents, because adolescents and children are considered to be more susceptible to air pollution than adults.This scale was initially developed in China, and evaluates knowledge about emission sources, health effects, and health protection measures [123].The authors discussed the limitations of the generalisability of this scale because the validation study was conducted in a single city.Further validation studies will be necessary in international settings.

Dimensions of perception
We summarised the key dimensions of perceptions related to health risks from air pollution.Both 'Perception/awareness of air quality' and 'Perception of health risk' were the most frequently evaluated dimensions of perception.Specifically, we found that the largest number of studies focusing on 'Perception/awareness of air quality' during the mid to late 2010s were conducted in Asia.This result may reflect that poor air quality was often visually perceived during this period in the study areas, and that the media provided more coverage about air pollution.Surprisingly, several studies did not report when the survey was conducted.The study period is one of the most important factors affecting perception, because perception of air quality and its health risks are affected by the air quality levels at the time the survey is conducted.Additionally, environmental regulations also affect people's perceptions.

Limitations
Several limitations of this scoping review should be considered.This review did not include non-English articles, unpublished articles, or grey literature.Regarding studies published before the 2010s, it is likely that some studies evaluating perceived health risk from air pollution were published in non-English languages, because air pollution was considered as a local issue.This may have influenced the results of the trends we observed in the region-specific categorisation.Additionally, there was considerable variation in the terms used to describe the perceived health risks related to air pollution.This makes the interpretation of the results difficult.To overcome this limitation, we extracted studies using validated scales.

Conclusion
In this scoping review, we explored published articles investigating the perception of health risks posed by air pollution, focusing on the measurement scales used.
Only nine studies used standardised scales to quantify individuals' risk perception.Spatial and temporal comparisons of the health risk perception of air pollution may facilitate the understanding of individuals' behaviours to prevent air pollution exposure and support air pollution policies.Thus, further development of standardised methods is needed.

Figure 1 .
Figure 1.Flow diagram for the process of article selection.

Figure 2 .
Figure 2. Annual number of articles by region between 1990 and 2022.

Table 1 .
Summary of the included studies.

Table 2 .
Key dimensions of health risk perception from air pollution.

Table 3 .
Studies that used scaled questionnaires.

Table 3 .
(Continued).Adolescent Haze-Related Knowledge Awareness Assessment Scale; BRFSS: Behavior Risk Factor Surveillance Systems; CCAHS: Chicago Community Adult Health Study; IMECA: ÍndiceMetropolitano de la Calidad del Aire [Metropolitan Index of Air Quality]; WHOQOL-BREF: World Health Organisation Quality of Life-Brief.

Table 4 .
The dimensions measured by scaled studies.